1. Field of the Invention
The present invention relates to a process for the manufacture of cycloalkyldimethanol by a direct hydrogenation of a starting compound selected from cycloalkyldicarboxylic acid and an alkyl ester compound thereof and, more particularly, it relates to a process for the manufacture of 1,4-cyclohexanedimethanol (hereinafter, referred to as 1,4-CHDM) from a starting compound selected from 1,4-cyclohexanedicarboxylic acid and an alkyl ester compound thereof. Further, the present invention relates to a method for regeneration of a catalyst and to a process of hydrogenation using the regenerated catalyst.
2. Discussion of the Background
Cycloalkyldimethanol such as 1,4-CHDM is useful in polyester paints and in synthetic fibers and synthetic resins of a polyester type and is used particularly as a material for resins and fibers having excellent thermal resistance, weather resistance, physical strength, etc. (Encyclopedia of Chem. Tech., Kirk-Othmer, Vol. 12, 4th. ed., pp.732-737 (1994), incorporated herein by reference).
In the past 1,4-CHDM has been made by a process in which dimethyl terephthalate is subjected to hydrogenation using a catalyst of Ru or Pd carried on alumina to give dimethyl cyclohexanedicarboxylate, and then a side chain of the resulting ester is subjected to a hydrogenation reaction in the presence of a Cu--Zn oxide catalyst, to manufacture 1,4-CHDM, as mentioned, for example, in JP-W-8-510686. In addition, in JP-A-6-228028 is described a process for the manufacture of 1,4-CHDM where dialkyl terephthalate is subjected to hydrogenation to give dimethyl 1,4-cyclohexanedicarboxylate, and then the side chain of the product is hydrogenated using a catalyst containing Ru and Sn to manufacture 1,4-CHDM.
On the other hand, with regard to a process for direct hydrogenation of an aliphatic carboxylic acid or carboxylic acid ester, methods where a catalyst containing ruthenium, platinum and tin have been proposed. For example, JP-A-7-165644 describes a method for the manufacture of 1,4-butanediol and tetrahydrofuran by hydrogenation of maleic acid and succinic acid; JP-A-10-175897 describes a method for the manufacture of 3-hydroxymethyl-1,6-hexanediol by hydrogenation of 1,2,4-butanetricarboxylic acid; and JP-A-10-306047 describes a method for the manufacture of 1,6-hexanediol by hydrogenation of a mixture of carboxylic acid and carboxylate including adipic acid and hydroxycaproic acid. In these references, there is no description of hydrogenation reactions of alicyclic carboxylic acids and, in addition, there is no description at all for a method of regenerating of a ruthenium catalyst having a reduced activity. The alicyclic carboxylic acids (which is a starting compound used in the present invention) has a structure having more steric hindrance than the aliphatic carboxylic acids which has been used as a starting compound. Therefore, the conventional known catalysts are not always applicable or it is predicted that the reactivity is reduced in the case of alicyclic carboxylic acids as compared with aliphatic carboxylic acids.
In the process of JP-W-8-510686, there are the disadvantages that an esterifying step is essential, since an ester is used as the starting material, and that relatively severe reaction conditions such as high temperatures and high pressures are used since a copper catalyst is used for hydrogenation of the side chain. The process of JP-A-6-228028 is not so satisfactory from an industrial view, in terms of the yield of 1,4-CHDM.
In methods where a ruthenium catalyst is used, ruthenium is expensive and, therefore, it is important to carry out such a process on an industrial scale so that not only is the activity of the catalyst retained for a long period of time, but also the catalyst having reduced activity is regenerated. Further, although 1,4-CHDM is usually obtained as a mixture of trans- and cis-compounds, polyester resins manufactured from trans-1,4-CHDM have superior properties and, accordingly, there has been a demand for increasing the ratio of the trans-compound in the product.